The technical field of this invention concerns monitoring and controlling hydrocephalus.
Hydrocephalus is a neurological condition caused by the abnormal accumulation of cerebrospinal fluid (CSF) within ventricles, or cavities, of the brain. Hydrocephalus, which can afflict infants, children, and adults, arises when normal drainage of CSF in the brain becomes blocked in some way. Blockage of the flow of CSF consequently creates an imbalance between the rate at which CSF is produced by the ventricular system and the rate at which CSF is absorbed into the bloodstream. This imbalance increases pressure on the brain and causes the brain's ventricles to enlarge. Left untreated, hydrocephalus can result in serious medical conditions, including compression of the brain, atrophy of neural tissues, impaired blood flow, coma, and death.
Hydrocephalus may be treated by surgically inserting a shunt system to divert the flow of CSF from the ventricle to another area of the body, such as the peritoneum or another location in the body, where CSF can be absorbed. Typically, shunt systems remove excess CSF using a two-part catheter system that includes a ventricular catheter and a drainage catheter. The ventricular catheter can have a first end that is inserted into the skull of a patient and disposed within the ventricle of a patient, and a second end that is typically coupled to the inlet portion of the shunt valve. The first end of the ventricular catheter can contain multiple holes or pores to allow the CSF to enter the shunt system. At the other end of the shunt system, the drainage catheter has a first end that is attached to the outlet portion of the shunt valve and a second end that is configured to allow CSF to exit the shunt system for reabsorption into the blood stream.
Generally, the shunt valve, which can have a variety of configurations, is effective to regulate the flow rate of fluid through the shunt system. In some shunt valve mechanisms, the fluid flow rate is proportional to the pressure difference at the valve mechanism. These shunt valve mechanisms permit fluid flow only after the fluid pressure has reached a certain threshold level. Thus, when the fluid pressure is slightly greater than the threshold pressure level, the fluid flow rate is relatively low, but as the pressure increases, the fluid flow rate simultaneously increases. Typically, the shunt valve allows fluid to flow normally until the intracranial pressure has been reduced to a level that is less than the threshold pressure of the shunt valve, subject to any hysteresis of the device.
Some shunt valves allow external adjustment of the threshold pressure level at which fluid flow will commence. For example, the shunt valve can contain a magnetized rotor to control the pressure threshold of the valve. A physician can then use an external adjustment mechanism, such as a magnetic programmer, to adjust the pressure threshold of the shunt valve. However, these magnetized rotors can be unintentionally adjusted in the presence of a strong external magnetic field, such as during a magnetic resonance imaging (MRI) procedure. Unintentional adjustment of the pressure threshold could lead to either the overdrainage or underdrainage of CSF, which can result in dangerous conditions, such as subdural hematoma.